ABSTRACT:Heat is transported by phonons through dielectric solids such as ceramics and organic insulating resins. Especially in organic insulating resins, phonons scatter intensely mainly by their amorphous structure, which affects their thermal conductivities, usually 1 to 3 orders lower than those of ceramics and metals. Here, we show that by the thermosetting resin system with a crystal-like structure that is microscopic anisotropy, the thermal conductivities of the resin themselves can be improved while keeping their macroscopic isotropy. We studied four kinds of diepoxy monomers with a biphenyl group or two phenyl benzoate groups as mesogens, and cured them thermally with an aromatic diamine curing agent. These thermal conductivities were maximally 5 times higher than that of conventional epoxy resins because mesogens were highly ordered to form crystal-like structures to suppress phonon scattering. We also succeeded in the direct confirmation of the existence of crystal-like structures in the epoxy resins by TEM observation. These results suggest a novel strategy to improve thermal conductivities of insulating resins themselves by controlling the high-order structures.

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To clarify the delamination mechanism of high‐voltage coil insulators made from mica flakes and epoxy resin due to static mechanical stress, the relationships between the shear strength of the insulator and the physical properties of the component materials were studied. The mechanism of their delamination was thought to be either a lack of epoxy resin between the mica flakes, interface failure between the mica flakes and the epoxy resin, or cleavage of the mica flakes. The first two mechanisms were discounted because the shear strength of the insulator was found to be independent of both the contact angle of the corresponding liquid epoxy resin on the mica flakes and the critical surface tension of the epoxy resin. Furthermore, the shear strength of the model insulator was improved by using an epoxy resin with a higher bending elastic modulus, implying that the delamination mechanism in this system is the cleavage of mica flakes. Therefore, the epoxy resin should have a high elastic modulus to ensure high delamination resistance, that is, the temperature to which the insulators are exposed should be lower than the glass transition temperature of the corresponding epoxy resin. Optical microscope studies also supported these results. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2164–2169, 2001

Both electric and electronic apparatus have recently been improving in size and performance with increasing heat quantity from inside and have large and important subjects to diffuse the heat efficiently in their design. Although resins are mainly used for insulating materials, they have quite low thermal conductivities, usually 1 ~ 3 orders lower than those of ceramics and metals, to greatly prevent the heat from diffusing. In this paper, we suggested a novel strategy to afford high thermal conductive thermosetting resins and confirmed it. We used several kinds of epoxy resin monomers with mesogens, and cured them with aromatic diamine curing agents. The thermal conductivities of epoxy resins containing biphenyl groups were 0.22 ~ 0.33 W/m•K that were a maximum 1.7 times higher than the conventional epoxy resin of 0.19 W/m•K, but the values were considered to be a limit in this system. To further improve the thermal conductivity, we made epoxy resins from the monomers containing two phenyl benzoate groups as mesogens. These epoxy resins had quite excellent thermal conductivities of 0.85 ~ 0.96 W/m•K that would be highest of all isotropic insulating resins. We also carried out the confirmations of high order structures of resins by TEM observation.